This application seeks support for a three-year study of procedures that may enhance discrimination learning and retention in mentally retarded individuals. We propose to compare reinforcement procedures that provide specific, discriminably different reinforcing consequences for different discrimination performances to procedures that provide a common reinforcer (or set of reinforcers) for such performances. Comparisons will be made with the conditional discrimination procedure known as matching to sample. A series of experiments will ask whether specific reinforcement procedures will (a) enhance retention of discriminations, tested in the delayed matching-to-sample format, and (b) facilitate acquisition of stimulus equivalence relations after conditional discrimination training. Additional studies will determine if specific reinforcers will (c) become members of the same stimulus classes as stimuli to be learned and remembered, and (d) support more rapid expansion of equivalence classes than is typically observed in mentally retarded individuals.